This invention relates to packaging materials useful for packaging a variety of articles and more particularly to packaging materials suitable for sealing the capped mouths of containers such as bottles for, e.g., wine, champagne and like alcoholic liquors, fruit juice drinks, sauces and like seasonings, etc. and to sealing caps made of such packaging materials.
Conventional seal caps over the closed mouths of containers such as glass bottles for wine, champagne or the like include those produced by spinning tin foils and those prepared from heat-shrinkable plastics films.
However, the seal caps of tin foils involve the following problems: (1) spinning of tin foils tends to wrinkle or buckle the foil, resulting in seal caps with an unseemly appearance as a whole and in difficulties in reading the characters or the like printed on the foil, (2) the manufacture of seal caps entails much labor and consequently high production costs, (3) the tin foil is difficult to fit around the mouths of bottles and thus the seal is unsatisfactory in reliability and safety, and (4) the seal cap, although made of tin, is low in metallic luster and thus less decorative in case of need for metallic luster.
The seal cap of heat-shrinkable plastics films have the drawbacks: (1) the plastics film is so low in shape retention as to be difficult to fit around the mouths of bottles, and (2) the film entirely lacks metallic luster and can not be used in case of need for metallic luster.
It may be thought that the foregoing drawbacks would be overcome by using a packaging material useful for decorative labels and having a metallic deposit over a heat-shrinkable plastics film. But such packaging materials have a heat-shrinkable film covered with heat-unshrinkable metal and thus cause various problems in heat treatment with hot water, water vapor or hot air, consequently far from remedying the defects.
More specifically, these packaging materials encounter the problems: (1) if the metallic coat is as hard as a metallic foil, the packaging material has reduced heat shrinkability or the metallic coat tends to wrinkle because of the rupture of bonding layer between the film and the metallic coat, and (2) the metallic coat as thin as e.g. a coat formed by vaccum deposition is likely to corrode or to partially peel off the film during heat shrinkage.